UNIT 13 Working with Versatile Lightweight Concrete

Read, translate the following text and be ready to fulfil the tests:

While still not light and resilient enough for a vehicle tire, properties of lightweight concrete lend creative architectural design possibilities to the realm of structural engineering. The properties of lightweight concrete have some remarkable advantages. While the term “lightweight concrete” sounds strange, the material itself is anything but contradictory. Regular Portland cement concrete production consists of loading aggregates (gravel and sand), cement, and water, then mixing to a thick slurry consistency. The mixing process usually incorporates a small amount of air into the concrete as well. Once the mix has cured it weighs in at around 145 pounds per cubic foot, give or take 5 pounds or so.

Most of this variation is due to the amount of air present and minor differences in the weight of the aggregates. Clearly, to make concrete lighter, more air and/or lighter aggregates need to be used. When more air or gas is incorporated, the result is referred to as lightweight aerated or foamed concrete. When lighter aggregates are loaded, the material is generically referred to as lightweight aggregate concrete. Lightweight aerated concrete typically weighs in between 3 pounds per cubic foot up to around 70 pounds per cubic foot. While this is still not suitable for a vehicle tire, it is tremendously useful for a wide variety of architectural applications. Due to the entrapped gases, it also has good insulating properties.

Roofing, walls, fences, ornaments, vaulted ceilings, sculptures, stairs, doors, even canoes are good examples of the usefulness of this material. It can be cast into blocks or decorative panels to create the impression of stone without the massive weight. And of course it still retains much of the durability of regular weight concrete. The major departure from regular concrete is lower structural and compressive strength.

Lightweight aggregates can consist of naturally occurring gas expanded materials such as vermiculite, pumice, certain volcanic rocks, and some diatomaceousearths. They can also be manufactured by heating some types of clay, shale, slate, and obsidian in a rotary kiln, or by using air quenched cinders and blast-furnace slag. These expanded aggregates incorporate air into a porous structure which retains some degree of structural strength. When used in structural concrete the mix has a density ranging from 90 pounds per cubic foot up to about 115 pounds per cubic foot.

However with a suitable mix design strengths similar to regular weight concrete can be attained. The major advantages of this material over regular concrete are lower densities, better fire resistance and greater insulating properties. Less reinforcing steel is required and a lower dead load of the structure can be achieved. This in turn yields smaller supporting columns, footings, and other engineering elements. It also results in improved seismic characteristics, longer achievable spans, thinner cross sections, and generally smaller sized structural members.

Read and memorize the active vocabulary to the text:

Active Vocabulary

1. vehicle tire автошина

2. lightweight легкий, облегченный

3. realm сфера, область

4. remarkable выдающийся, замечательный

5. contradictory противоречивый, несовместимый

6. aggregate заполнитель

7. slurry жидкое цементное тесто

8. to incorporate смешивать, соединять в одно целое

9. to cure исправлять; затвердевать

10. foamed вспененный

11. generically в общем

12. suitable подходящий, соответствующий

13. to entrap уловить, захватить

14. insulating изоляционный

15. vaulted сводчатый, арочный

16. durability прочность, долговечность

17. departure (здесь) отличие, отклонение

18. vermiculite (минералогия) вермикулит

19. diatomaceous earth (минералогия) диатомит

20. quenched закаленный, быстро охлажденный

21. blast-furnace slag доменный шлак

22. achievable достижимый

CONTROL TESTS

TEST I

Decide whether these statements are true or false:

1. a). Properties of lightweight concrete retain much of the durability of regular weight concrete.

b). Properties of lightweight concrete lend creative architectural design possibilities to the realm of structural engineering.

c). Properties of lightweight concrete allow to use it for roofing, walls, fences, ornaments, vaulted ceilings, sculptures, stairs and so on.

2. a). When more air or gas is incorporated, the result is referred to as lightweight aerated or foamed concrete.

b). When more air or gas is incorporated, the result is referred to as lightweight aggregate concrete.

c). When more air or gas is incorporated, the result is referred to as concrete with a thick slurryconsistency.

3. a). The major departure from regular concrete is lower structural and compressive strength.

b). The major departure from regular concrete is lower construction material cost.

c). The major departure from regular concrete is greater insulating property.

4. a). Lightweight aggregates can consist of naturally occurring gas expanded materials.

b). Lightweight aggregates can consist of more air or gas incorporated.

c). Lightweight aggregates can consist of the entrapped gases.

5. a). The major advantage of this material over regular concrete is its weight between 3 pounds per cubic foot up to 70 pounds per cubic foot.

b). The major advantages of this material over regular concrete are lower densities and better fire resistance.

c). The major advantage of this material over regular concrete is usefulness for a wide variety of architectural applications.

TEST II

Match words in columns A and B (synonym match):

A B

1. resilient a). relevant b). previous

c). flexible d). elastic

2. property a). evidence b). feature

c). report d). discrepancy

3. advantage a). division b). statute

c). benefitd). increase

4. contradictory a). inconsistent b). durable

c). ready d). necessary

5. to incorporate a). to indicate b). to combine

c). to identify d). to irritate

6. tremendously a). originally b). automatically

c). enormously d). precisely

7. difference a). inequality b). durability

c). extrusion d). constituent

8. resistance a). support b). counteraction

c). activity d). purpose

9. suitable a). fitting b). auxiliary

c). capable d). preventive

10. similar a). rigid b). decisive

c). stable d). resembling

TEST III

Select the best possible answer out of the choices from the list to the statements (multiple choice):

1. The mixing process of lightweight concrete usually … .

a. needs heating some types of aggregates.

b. results in a thick slurryconsistency.

c. incorporatesa small amount of air into the concrete.

d. makes it resilient enough for a vehicle tire.

2.Lightweight aggregates can consist of … .

a. such materials as gravel and broken stone.

b.such materials as lime, calx and sand.

c. such materials as slag and sinter.

d. gas expanded materials such as vermiculite, pumice, volcanic rocks, etc.

3. Due to the entrapped gases, … .

a. lightweight concrete has high structural and compressive strength.

b. lightweight concrete also has good insulating properties.

c. lightweight concrete has the cooling effect on dwelling houses.

d. lightweight concrete is resilient enough for pavements.

4. Lightweight concrete retains … .

a. much of the durability of regular weight concrete.

b. high construction material costs.

c. all structural possibilitiesof regular weight concrete.

d. high strength and density of regular weight concrete.

5.The properties of lightweight concrete … .

a. are higher structural and compressive strengths.

b. imply the use ofmore reinforcing steel.

c. have some remarkable advantages.

d. include a higher dead load of the structure, that can be achieved.

TEST IV